Conventional display apparatus, such as a neon sign tower, have drawbacks such as: (1) requiring a larger area than the characters and figures to be displayed, (2) difficulties in carrying and transporting the apparatus, (3) high lighting expense such as for electricity and (4) high cost of the apparatus.
Furthermore, signals and barriers used for construction and police work only perform a lighting function and cannot produce characters and figures in two-dimensional space.
As the size of an image display becomes larger, the size and weight of the signal apparatus increases, which means an increase in manufacturing cost and maintenance expense.